The use of phenolic resins for solid castings, solid moldings and coating films is well known in the coatings and resins industry. Additionally free rise foams made from phenolic resole resins are known. Although the use of phenolic foams would appear to be attractive for potential use in thermal insulation applications, such use has been severely limited by the generally inferior insulating properties of known phenolic foams as compared, for example, to polyurethane foams.
The thermal insulating ability of a foamed material generally may be evaluated by thermal conductivity or "K factor." The thermal conductivity or K factor of a particular insulation material is measured according to ASTM Method C-518 Revised, and is expressed dimensionally as (BTU.times.inch)/(hour.times.square foot.times..degree. F.). The lower the K factor, the better is the insulating quality of the insulation material. Additionally, the longer the material such as a foam insulation can retain a low K factor, the better is the insulating efficiency of the material with time.
Generally known phenolic foams produced from compositions of phenol-formaldehyde resole resins, acid catalysts, surfactants and blowing agents suffer from generally unacceptable initial K factors and their inability to retain a low K factor over an acceptable period of time.
Although the specific reasons for both generally poor initial K factor and increase in K factor with time are largely unknown, they are believed to be at least in part attributable to such factors as the percentage of closed cells in the phenolic foam and the ability of the cell walls to inhibit the outward diffusion from the cells of trapped gases used as blowing agents and the inward diffusion of components of air into the cells.
The present invention is directed to a method for producing phenolic foams having improved properties as will become apparent in the discussion following. The invention also is directed to foams produced using the method of the invention.